Hmm, strange. Indeed, many dictonaries say it's a dark-blue color. http://www.onelook.com/?w=cyan&ls=a
From: "Timothy A. Gregory" Subject: RE: Translation question Date: Thu, 17 Apr 2003 21:27:06 -0400
Al-Mughni Al-Akbar gives أزرق قاتم, and http://tarjim.ajeeb.com gives أزرق داكن for cyan.
HTH
--tag